Gout de Souris

Gout de souris …

Mouse taint. In Spanish, rat taste. Something similar in German.
There are many ways in which wine can become unpalatable. TCA (cork taint), madeirisation or oxidation, volatile acids, bret. Some of them can at times lend charm to the wine, or add something particular – sherry and madeira, or vin jaune from Jura, will more often than not have notes of oxidization. Old, traditional Bandol smelling like a stable is afflicted with brettanomyces and may be the better for it (possibly). No one, on the other hand, ever claimed TCA added something of value to a wine. And now comes le gout de souris.

In the hospitable home of good friends Jan and Barbro we were having a tasting of the wines of Mas Zenitude, led by none other than the winemaker himself, Erik Gabrielsson, and his lovely wife Francee, who is also in the wine trade. After going through 6 wines, he passed a seventh around the table, saying, Beware – this one has “le gout de souris”. Which indeed it did, and a friendly argument broke out concerning this mysterious taint. Erik mentioned that it would pass, on cellaring (possibly true), and raised the hypothesis that it was due to some kind of oxidation (not exactly).

The taint has apparently been known for a long time but, been away due to the addition of sulfites to wine. Then, however, came the natural wines where addition of sulfite was seen as detrimental. Not all natural wines have it, of course, nor even all bottles from the same batch. It appears also that the taint may disappear over time.

It has been described as the smell of a mouse cage, sometimes a bit like popcorn (doesn’t sound as bad). It is alos pointed out that it is not a direct smell, you do not smell it by sniffing at your glass (I am not entirely in agreement), but, it is a retronasal smell, meaning, you do not immediately perceive it on introducing the wine in your mouth, rather, you may even swallow it, and the odor, or aroma, will appear over time. You can also dip your finger in the wine and rub on your hand – when it has dried, the smell will appear.

Three different compounds cause the mousy flavors [1]: 2-ethyltetrahydropyridine, 2-acetyltetrahydopyridine [7], and 2-acetylpyrroline. These compounds are metabolites of two amino acids, lysine, and ornithine. The metabolizers are either yeasts of the brettanomyces family, or bacteriae, either of the lactobacillus or the oenococcus strains, or, even worse, both. Apart from the amino acids, ethanol, or ethanol (acetaldehyde) and certain metal ions must be present. It is possible to demonstrate the synthesis of these compounds in a controlled manner [2].

Oddly, it appears the 2-acetylpyrroline is also the substance that gives the pleasant flavor to basmati rice [3], [6]. It would of course not be the only example of a substance that will, in some circumstances smell pleasantly, while in others be foul – remember that the passion fruit flavor of NZ Sauvignon Blanc comes from a thiol, compounds that normally gives associations of rotten eggs et c.

According to some sources, upwards of 30 % are insensitive to this taint [4].

The reason the odor is not immediately perceptible is that the wine is acidic, and the compounds in this environment are not volatile. Only in the mouth, as the wine’s acidity is balanced by the alkaline saliva, will it appear [5].

The taint may also disappear over time (meaning several months), but why that is, is not understood.
Oddly, some find the aroma appealing [idem]. The present writer does not.

For my last wine tasting, I presented, amongst others, a wine made from the rather rare Loire grape variety, pineau d’aunis, called Adonis. I had tasted this two months earlier and was extremely pleased with it, very fresh, with a slight white pepper edge to it – it had been suggested as an example of a “nervous wine”.
At the tasting, all the bottles were afflicted with mouse taint. Since the bottles were of the same provenience, this might indicate the short time span during which the taint might appear – more observations are needed.

During later years, it appears the cork taint has been gradually disappearing: it is not as common as it was ten years ago. A chlorine-free treatment of the corks may be the reason, and that is for the good. What to do about mouse taint?

The great Morgon wine maker Foillard would be considered a nature wine maker, if I understand him correctly: I have never found mouse taint in any of his happily imbibed bottles.

Prevention is advocated. A meticulous hygiene in the cellar and during bottling is of the utmost importance. I suspect it may not be enough. The action of both yeasts and bacteriae will be blocked by a judicious addition of sulfites (or SO2), but that is not palatable to nature wine makers.
I find a small amount of sulfite more palatable than mouse taint. I would ask what we lose by using small amounts of sulfite – if it is mouse taint, volatile acids, and premature oxidation, I would be all in favor. My reference is the completely fictitious halachic verdict of the Rabbi Hillel: “If the wine tastes good, drink it; if it tastes foul, do not. All else is commentary”.